Many electronic devices on the market today often use power converters to convert electric energy from one form to another (e.g., converting between alternating current and direct current), converting a voltage or current of an electrical signal, modifying a frequency of an electrical signal, or some combination of the above. Examples of power converters may include boost converters and buck converters. Such power converters are often used to convert an input voltage for other circuitry, wherein such converted voltage is greater than (e.g., if a boost converter is used) or less than (e.g., if a buck converter is used) the input voltage. A switching direct current-to-direct current (DC-DC) converter is a type of electronic circuit that converts a source of power from one DC voltage level to another DC voltage level. Examples of such switching DC-DC converters include but are not limited to a boost converter, a buck converter, a buck-boost converter, an inverting buck-boost converter, and other types of switching DC-DC converters.
FIG. 1A illustrates an example synchronous switching DC-DC buck converter 100, as is known in the art. Buck converter 100 may include a switch 1, a switch 2, an inductor 104, and a capacitor 106 coupled in the manner shown in FIG. 1A. When switch 1 is closed, an input voltage supply 102 may provide a DC voltage to inductor 104, and when switch 2 is closed, an inductor 104 may discharge to a ground voltage. In typical operation, a switch control circuit controls the turn-on times and turn-off times of switches 1 and 2, and a current is maintained in inductor 104 to transfer energy from the input voltage supply 102 to the output voltage 108, such that output voltage 108 is smaller than the input voltage of input voltage supply 102.
FIG. 1B illustrates an example synchronous switching DC-DC boost converter 100B, as is known in the art. Boost converter 100B may include a switch 1B, a switch 2B, an inductor 104B, and a capacitor 106B coupled in the manner shown in FIG. 1B. An input voltage supply 102B may provide a DC input voltage to boost converter 100B, and in typical operation, a switch control circuit may control the turn-on times and turn-off times of switches 1B and 2B in order to maintain a current in inductor 104B to transfer energy from the input voltage 102B to the output voltage 108B, such that output voltage 108B is larger than the input voltage of input voltage supply 102B.
In order to correctly control switching of the switches shown in the converters of FIGS. 1A and 1B (e.g., buck converter 100 and boost converter 100B), and thus provide a desired output voltage (e.g., 108, 108B), the current through the inductor (e.g., 104, 104B) of the converter may need to be measured. In addition, measurement of current through the inductor of a converter may be used for other purposes, including compensation, operating mode detection, or inductor over-current detection. Example measurement techniques, as are known in the art, are illustrated in FIGS. 2A through 2C for measuring an inductor current in a buck converter. Similar and analogous measurement techniques, although not illustrated herein, may also be applied to other types of converters, including a boost converter, buck-boost converter, and inverted buck-boost converter.
FIG. 2A illustrates an example switching DC-DC converter topology 200A, as is known in the art. As shown in FIG. 2A, topology 200A may include a precision voltage measurement circuit 202A and a resistor 204A. Switching DC-DC converter topology 200A may be similar in topology to buck converter 100 except that a resistor 204A with a known resistance may be coupled in series with inductor 104. Precision voltage measurement circuit 202A may be coupled to resistor 204A as shown in FIG. 2A to measure a voltage across resistor 204A. From the measured voltage across resistor 204A, the current through inductor 104 may be calculated. However, there may be disadvantages with the measurement technique depicted in FIG. 2A. One disadvantage may be power loss through resistor 204A. Another drawback is that precision voltage measurement circuit 202A may require precision analog circuitry in order to obtain accurate measurements, and thus, measuring the voltage across resistor 204A requires a separate precision analog circuit that involves high precision voltage measurements, which may add cost and complexity to a system.
FIG. 2B illustrates another example switching DC-DC converter topology 200B, as is known in the art. As shown in FIG. 2B, topology 200B may include a precision voltage measurement circuit 202B, a resistor 204B, and a capacitor 206. Switching DC-DC converter topology 200B may be similar in topology to buck converter 100 except that a resistor and capacitor network comprising resistor 204B and capacitor 206B may be coupled in parallel to inductor 104 as shown in FIG. 2B. Precision voltage measurement circuit 202B may be coupled to capacitor 206 as shown in FIG. 2B to measure a voltage across capacitor 206. As may be recognized by those of skill in the art, a voltage across capacitor 206 may be proportional to the inductor current through inductor 104. However, there may be disadvantages with the measurement technique depicted in FIG. 2B. For example, a resistor-capacitor network used in topology 200B may require a large integrated circuit area. Another disadvantage may be that resistor 204B and capacitor 206 of the resistor-capacitor network and their respective impedances may be susceptible to manufacturing process variations, which in turn may lead to inaccurate measurements.
FIG. 2C illustrates another example switching DC-DC converter topology 200C, as is known in the art. As shown in FIG. 2C, topology 200C may include a switch current measurement circuit 202C. Switching DC-DC converter topology 200C may be similar in topology to buck converter 100 except that switch current measurement circuit 202C may be coupled inline between input voltage source 102 and switch 1 as shown in FIG. 2C. Accordingly, switch current measurement circuit 202C may measure a current carried through switch 1. As may be recognized by those of skill in the art, the current through inductor 104 is the same as the current through switch 1 when switch 1 is closed. However, there may be disadvantages with the measurement technique depicted in FIG. 2C. For example, in many implementations, switch current measurement circuit 202C may be an analog circuit that may be susceptible to large errors in its measurements and may also consume relatively large amounts of power (e.g., may consume current in the order of a few hundred micro-amps). In addition, in implementation when a switching control circuit provides digital control of switching DC-DC converter topology 200C, the inductor current signal through inductor 104 may first need to be converted to a digital signal before it is used by the switching control circuit. Accordingly, this measurement approach may require an analog-to-digital converter (“ADC”) to convert the analog signals to digital signals, which may consume a relatively large amount of power.
FIG. 3 illustrates an example inductor current waveform 300 for switching DC-DC converter (e.g., converter 100, converter 100B) operating in continuous conduction mode (“CCM”), as is known in the art. As seen in FIG. 3, the inductor current is periodic with a switching period T. To regulate an output voltage (e.g., 108), a switch control circuit causes a first switch (e.g., switch 1) to close to for a time ton1 while causing a second switch (e.g., switch 2) to remain open, after which the switch control circuit causes the second switch to close for a time ton2 while causing the first switch to remain open, such that T=ton1+ton2. An output voltage Vout (e.g., output voltage 108) and an input voltage Vin (e.g., provided by input voltage source 102) may, in a buck converter, satisfy the relationship Vout/Vin=ton1/(ton1+ton2).